This Program Project forms the basis for the coordinated research in the Division of Clinical Immunology and Rheumatology. These laboratories involve biochemistry, immunopathology, immunophysiology, collagen structure and cell surface biology. The various areas that are currently under study include: 1) The structure of IgM and its role in complement fixation; 2) The basis for J-chain attachment to polymeric immunoglobulins, including the primary structure of J-chain and intrachain disulfide bonding; 3) Model systems of inflammation, that parallel clinical complement and immunoglobulin studies in man; 4) Clinical detections of immune complexes and their clinical importance in rheumatic diseases as well as in inflammatory vasculitic states associated with malignancy; 5) The isolation and structure of cell surface antigens, particularly those that might have relationship to clinical syndromes. It should be noted that these investigations form the center of our clinical research and patient care activities. Questions that arise from specific problems of patient care are analyzed by the various approaches included in this Coordinated Study in Rheumatic Diseases.